Destruction Technologies for Polychlorinated Biphenyls

4. Destruction Processes

4.5 Physical/Chemical Processes

• 4.5.1   Physical/Chemical Extraction Companies

Unlike all of the other process types considered previously, physical/chemical processes for handling PCBs are not treatment or destruction. In all of these processes, PCBs are extracted from transformers and replaced with another fluid. This does not help get rid of the PCB problem it just changes its location. The PCBs must still be treated or disposed of by some appropriate means.

These "extraction" processes use known and well tested chemical or physical methods for extraction of organic compound from another medium. Methods can range from the very simple physical process of thoroughly draining a PCB-filled transformer and replacing with an non-PCB-containing dielectric fluid to the more complex chemical processes such as distillation of the PCB from the transformer fluid or shredded capacitors.

There are over a hundred companies in the United States and four or five in Canada who are in the business of extracting PCB-contaminated fluids from transformers. Many of these are in the transformer service or maintenance business and only extract PCBs from transformers when there is a leakage or a functional problem. These companies will generally not take responsibility for the treatment/destruction/disposal of the PCBs after removal. There are other companies such as SED Inc., in the United States, who are in the business of extracting PCBs from transformers, taking over responsibility for disposing of the PCBs by government approved methods and then disposing of them.

4.5.1 Physical/Chemical Extraction Companies

* transport to US for treatment is dependant on the pending approval by the US and Canadian governments to reopen the border to PCB transport.

All of these companies are approved to handle PCBs in Canada.

4.6 Bacterial Degradation of PCBs in Soils

• 4.6.1   PCB Adapted Bacterial Cultures

Analysis of attempts at PCB degradation using soil bacteria showed that this degradation method was of limited potential due to long residence times, etc. A brief review of degradation by soil bacteria is included for completeness.

PCBs are extremely resistant to acid and base hydrolysis and oxidation. Their stability varies with the position of the chlorine substitutions but generally increasing with increasing chlorine content.

This structural relationship also holds for the resistance of PCBs to bacterial degradation. Mono- and dichloro-biphenyls have been readily biodegraded by activated sludge bacteria in a matter of days at low concentrations, higher concentrations taking longer. Trichlorobiphenyl degraded more slowly, tetrachlorophenyls were only slightly affected and pentachlorobiphenyls were unaffected.

This stability-structural relationship is borne out by the observation that Aroclors are fractionated in soils; the less chlorinated isomers disappearing first. PCB isomers may be categorized by degradation rate as follows:

Group A

Species containing two or less chlorine atoms, degrading rapidly with a half-life of eight days and 90% destruction in 15 days (Aroclor 1221, 1232).

Group B

Many tri- and tetrachlorobiphenyls. Half lives range up to 30 days, with 90% destruction in up to 60 days or more (Aroclor 1242, 1248 and components of 1254).

Group C

Penta - and greater substituted biphenyls. Half-lives are over a year. (Aroclor 1260 and components of 1254).

There is little quantitative data about the fate of biphenyls with seven, eight or nine chlorinated sites but they are considered much more persistent than Group C.

The slow destruction of PCBs in the environment may be outstripped by the evolution of micro-organisms able to degrade even the higher chlorinated PCBs. As a result, soils show limited potential for PCB destruction, although it may be developed, particularly by seeding with PCB adapted cultures.

References: (Farquhar and Sykes, 1978; Brooks, 1979; Iwata et al., 1974; Yagi and Sudo, 1980; Pat et al., 1980).

4.6.1 PCB Adapted Bacterial Cultures

Polybac Corporation
1251 South Cedar Crest Boulevard
Allentown, Pennsylvania 18103

Contact: Curtis S. McDowell, Vice President

Polybac Corporation has developed a series of mutant bacteria products which are capable of destroying chemicals in soil. One such mutant bacteria product is capable of degrading polychlorinated biphenyls i.e., PCBs.

The mutant bacteria products that Polybac Corporation manufactures are applied to the soil contaminated with PCBs in conjunction with an emulsifying agent. The soil is cultivated and kept moist for the duration of the degradation time required for PCBs.

Laboratory research reported in the open literature has demonstrated the biodegradability of several PCB mixtures by bacteria. For example, 99.8% destruction of 300 ppm Aroclor 1254 was achieved in 18 days. Polybac mutant bacteria have been shown to degrade a number of PCB isomers.

Polybac has been using mutant bacteria to biodegrade chemicals in soils for many years. Testing of the applicability of mutant bacteria to PCB degradation is quite recent and further testing is required to determine the efficiencies obtainable.

Bacterial degradation of PCBs is a process that works efficiently on less chlorinated biphenyls and offers a low cost alternative to excavation and landfill.

Reference: (Manufacturer's literature)